This invention relates to distributed computing systems using data communications networks, and more particularly to methods of providing configuration information to clients in a distributed computing system regarding network services or remote procedure calls.
In U.S. Pat. No. 4,823,122, issued Apr. 28, 1989, assigned to Digital Equipment Corporation, assignee of this invention, a communications network is disclosed which is capable of interconnecting local computer terminals with remote service providers using a communications link. The local terminals are coupled to the communications link by interface units which handle network protocol functions for the terminals. One of the functions necessary at the local units is that of obtaining actual network addresses for services known locally only by service names. To perform this translation, service advertisements are periodically sent by the service providers, and a service directory is generated locally from these advertisements. Then, when a service request is generated locally, the service directory is searched to find the corresponding network address of the provider of this service. If there are multiple providers of the same service some mechanism must be provided for selecting the most efficient service provider for a local requester, and for distributing the load among the various providers in an efficient manner.
In U.S. patent application Ser. No. 314,853, filed Feb. 24, 1989, now U.S. Pat. No. 5,341,477, by Richard P. Pitkin and John C. Morency, for "Broker for Computer Inventory Server Selection", a method is disclosed for allocating resources within a computer network by employing a broker mechanism. This broker mechanism operates by monitoring a subset of all available servers capable of delivering the requested service, and allocating based upon a network policy and available resources, to suggest the name of a provider to a service requester.
There are often redundant resources in a distributed system, in order to improve availability and share load. One problem faced by a user (i.e., an applications programmer) in such an environment is selecting a particular resource for use. The user would ideally like means of selecting an instance of a redundant resource that preserves the availability and load sharing, yet may be optimized to the particular environment and/or tailored to the user preferences. For example, when using an remote procedure call service (the resource) that supplies an employee address list, the remote procedure call user may prefer resources within the same LAN, with high speed communications available, to be selected in preference to resources available only via a wide area network. However, if the resources in the local LAN are not available, the remote procedure call user would like to use the remote resources accessible only via the wide area network. Furthermore, the designation of local and remote is relative. Each user, possibly in a different location, may have different views of what is local and what is remote. Therefore, the selection of resources must be able to be tailored to the user and or conditions local to the user.
An objective, then, in a system having redundant distributed resources, is to provide a mechanism that supports the customized selection of resources in a distributed environment, while maintaining availability and load sharing.